[PATCH v9 2/5] vfio: selftests: Add helpers to re-enable interrupts

[Josh Hilke <jrhilke@google.com>]

From: Alex Williamson <alex.williamson@nvidia.com>

Selftest drivers that recover from a fault by issuing VFIO_DEVICE_RESET
need to re-arm device interrupts afterwards.  VFIO_DEVICE_RESET tears
down the kernel-side IRQ trigger so a subsequent VFIO_DEVICE_SET_IRQS
is required, but the user-side eventfds (and any fd cached in a test
fixture) are still valid and must be preserved.

vfio_pci_irq_enable() refuses to be called for vectors that already
have an eventfd (VFIO_ASSERT_LT), and vfio_pci_irq_disable() closes
all eventfds before resetting the trigger, so neither is suitable.

Add vfio_pci_irq_reenable(device, index, vector, count) which asserts
that the requested range has existing eventfds and re-issues
VFIO_DEVICE_SET_IRQS using them.  Signature mirrors vfio_pci_irq_enable().

Add vfio_pci_msi{,x}_reenable() wrappers around vfio_pci_irq_reenable()
for additional ease of use and readability.

Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Alex Williamson <alex.williamson@nvidia.com>
Reviewed-by: David Matlack <dmatlack@google.com>
---
 .../vfio/lib/include/libvfio/vfio_pci_device.h     | 14 ++++++++++++++
 tools/testing/selftests/vfio/lib/vfio_pci_device.c | 22 ++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/tools/testing/selftests/vfio/lib/include/libvfio/vfio_pci_device.h b/tools/testing/selftests/vfio/lib/include/libvfio/vfio_pci_device.h
index 59acef381d05..89a039ab3075 100644
--- a/tools/testing/selftests/vfio/lib/include/libvfio/vfio_pci_device.h
+++ b/tools/testing/selftests/vfio/lib/include/libvfio/vfio_pci_device.h
@@ -84,6 +84,8 @@ static inline void vfio_pci_cmd_clear(struct vfio_pci_device *device, u16 bits)
 void vfio_pci_irq_enable(struct vfio_pci_device *device, u32 index,
 			 u32 vector, int count);
 void vfio_pci_irq_disable(struct vfio_pci_device *device, u32 index);
+void vfio_pci_irq_reenable(struct vfio_pci_device *device, u32 index,
+			   u32 vector, int count);
 void vfio_pci_irq_trigger(struct vfio_pci_device *device, u32 index, u32 vector);
 
 static inline void fcntl_set_nonblock(int fd)
@@ -108,6 +110,12 @@ static inline void vfio_pci_msi_disable(struct vfio_pci_device *device)
 	vfio_pci_irq_disable(device, VFIO_PCI_MSI_IRQ_INDEX);
 }
 
+static inline void vfio_pci_msi_reenable(struct vfio_pci_device *device,
+					 u32 vector, int count)
+{
+	vfio_pci_irq_reenable(device, VFIO_PCI_MSI_IRQ_INDEX, vector, count);
+}
+
 static inline void vfio_pci_msix_enable(struct vfio_pci_device *device,
 					u32 vector, int count)
 {
@@ -119,6 +127,12 @@ static inline void vfio_pci_msix_disable(struct vfio_pci_device *device)
 	vfio_pci_irq_disable(device, VFIO_PCI_MSIX_IRQ_INDEX);
 }
 
+static inline void vfio_pci_msix_reenable(struct vfio_pci_device *device,
+					  u32 vector, int count)
+{
+	vfio_pci_irq_reenable(device, VFIO_PCI_MSIX_IRQ_INDEX, vector, count);
+}
+
 static inline int __to_iova(struct vfio_pci_device *device, void *vaddr, iova_t *iova)
 {
 	return __iommu_hva2iova(device->iommu, vaddr, iova);
diff --git a/tools/testing/selftests/vfio/lib/vfio_pci_device.c b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
index 28868343f2ab..65a4fffb480c 100644
--- a/tools/testing/selftests/vfio/lib/vfio_pci_device.c
+++ b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
@@ -105,6 +105,28 @@ void vfio_pci_irq_disable(struct vfio_pci_device *device, u32 index)
 	vfio_pci_irq_set(device, index, 0, 0, NULL);
 }
 
+/*
+ * Re-issue VFIO_DEVICE_SET_IRQS for an already-enabled vector range using
+ * the existing eventfds.  Intended for drivers that need to re-arm device
+ * interrupts after a VFIO_DEVICE_RESET, which tears down the kernel-side
+ * IRQ trigger but leaves user-side eventfds intact.  Recreating the
+ * eventfds would invalidate any test-fixture cache of the fd, so this
+ * helper deliberately preserves them.
+ */
+void vfio_pci_irq_reenable(struct vfio_pci_device *device, u32 index,
+			   u32 vector, int count)
+{
+	int i;
+
+	check_supported_irq_index(index);
+
+	for (i = vector; i < vector + count; i++)
+		VFIO_ASSERT_GE(device->msi_eventfds[i], 0,
+			       "vector %d eventfd not allocated\n", i);
+
+	vfio_pci_irq_set(device, index, vector, count, device->msi_eventfds + vector);
+}
+
 static void vfio_pci_irq_get(struct vfio_pci_device *device, u32 index,
 			     struct vfio_irq_info *irq_info)
 {

-- 
2.55.0.508.g3f0d502094-goog